The invention relates to an over-center hinge for cabinet doors, in which one of the parts has a mortise cup made of plastic, from whose circumferential wall a tongue which is integral with the mortise cup, projects diagonally into the interior of the mortise cup and can yield against spring bias, and on which a contact surface provided on the other hinge part at its end facing the pivot glides during a portion of the swing of the hinge and is movable in an intermediate position through a dead center on one side of which it urges the door to the closed position and on the other side of which it exerts a pressure in the opening direction, the contact surface being so disposed that in the closed position it is situated in the immediate vicinity of the pivot axis of the tongue.
An older hinge of this kind is known (German Pat. No. 2,016,398) in which the tongue, stiffened on its back by ribs, lies in a cut-out in the circumferential wall, merging integrally at its bottom end with the bottom of the mortise cup. The spring force of the tongue holding the hinge in the closed position is produced in this hinge by the resilient flexing of the area where the bottom and tongue join, which simultaneously forms the pivot axis of the tongue, and by an elongated, curved leaf spring injection molded on the upper end of the tongue. This hinge has proven practical on account of its good door-holding power resulting from the favorable leverage ratio in the closed position. Since the mortise cup is made in one piece with the tongue out of plastic, it is also relatively inexpensive. In the case of hinges for heavy doors, however, where an especially strong holding power is required, the leaf spring assisting the spring force of the tongue has to be relatively long, so that the leaf spring support opposite the tongue has to be disposed at a considerable distance outside of the mortise cup. For this reason, a relatively elongated flange is provided on the side of the mortise cup away from the hinge pivot, and on it the leaf spring is supported. The relatively compact dimensions of the mortise cup resulting from the arrangement of the tongue within the cut-out in the circumferential wall are thereby increased, and this is not desirable, inasmuch as the projecting flange and the leaf spring are visible when the door is open and they project the inside surface of the door. In certain, though rare, cases, the flexing of the tongue, which is substantially limited to the area where the bottom end of the tongue joins the bottom of the mortise cup, has caused the tongue to break off from the bottom as the plastic material becomes aged and embrittled, so that in a later period the manufacturers ceased to mold the tongue in one piece in this area with the floor of the mortise cup, and instead a separate pivot eye was provided on the tongue, which was then mounted in the cup with a pivot pin (German Pat. No. 2,122,857). This, however, complicates and increases the cost of the manufacture of the mortise cup on account of the pivot pin and the installation thereof.